具等能量密度之精微線切割放電加工電源於工件輪廓精度改善研究

Abstract

本研究旨在開發一應用於精微線切割放電加工具「等能量密度」的放電電源，以改善工件轉角處因能量密度過度集中所導致的加工誤差問題。放電能量的過度集中，可能會造成輪廓過切或讓切情形，尺寸精度易發生誤差且輪廓精度失真，造成精微元件缺損。為維持精微工件的輪廓精度，本研究提出一種「位置同步輸出(Position Synchronized Output, PSO)」的技術，CNC控制系統所產生的連續位置訊號，經由元件可程式邏輯閘陣列(Field Programmable Gate Array, FPGA)轉換，以便控制高頻等脈衝微放電的正確輸出距離，達到等能量密度的精微線切割放電加工。實驗以超微粒碳化鎢為材料進行轉角精度加工，結果顯示，在放電電容2000 pF、放電頻率800 kHz、加工進給率0.04 mm/min的加工條件下，當位置同步輸出機能啟動時，以0.03 μm的開啟距離有最顯著的改善效果，其在內、外轉角處的加工誤差分別可從10.22 μm及6.26 μm降至2.77 μm及0.92 μm。本研究以擺線齒形微結構進行加工驗證，擺線齒形微結構之齒厚與齒間的加工誤差皆小於1 μm，證實位置同步輸出機能輔助加工能獲得穩定且高一致的放電能量密度。顯見本研究所開發的「具等能量密度之放電電源」可使放電能量密度隨加工路徑的距離進行均勻化分佈，減少工件材料轉角處被過度熔蝕的現象，維持工件輪廓的完整性及尺寸的精確性。這項研究成果能改善精微元件的形狀精度，值得商業化。The purpose of this study is to develop a discharge power source with"equal energy density" applied to the micro w-EDM, so as to improve the machining error caused by the excessive concentration of energy density at the corners of the workpiece. Excessive concentration of discharge energy is likely to cause the workpiece contour either over-cut or under-cut situations, the dimensional accuracy is prone to error and incorrect contouring accuracy resulting in defects of microparts. In order to maintain the contour accuracy of micropart, a "Position Synchronized Output (PSO)" technology, in which the continuous position signal generated by the CNC system is converted by the Field Programmable Gate Array (FPGA) is proposed in this study to control the correct discharge distance of the high-frequency ISO-pulsed micro-discharge, achieving the micro wire-cut discharge technology with the same energy density. The experiment uses ultra-fine tungsten carbide as the material for corner precision machining test. The result show that the most significant improvementeffect can be achieved when the PSO function with the distance of 0.03 μm is enabled and under the machining conditions of discharge capacitance of 2,000 pF, discharge frequency of 800 kHz, and machining feed-rate of 0.04 mm/min. The machining errors at the inner and outer corners can be reduced from 10.22 μm and 6.26 μm to 2.77 μm and 0.92 μm, respectively. The cycloid gear microstructure is used for machining verification. Experimental results show that the machining errors of tooth thickness and tooth pitch of the cycloid gear microstructure is all less than 1 μm, and it is proved that the PSO function assisted the machining to obtain stable and high-consistent discharge energy density. It is evident that the discharge power source with"equal energy density" developed in this study can evenly distribute the discharge energy density with the distance of the machining path, reducing the phenomenon of over-cut and under-cut at the corners of the workpiece, which maintains the integrity of the workpiece contour and dimensional accuracy. The research result is worthy of commercialization due to the improvement of form accuracy of micropart.